Four objectives of trolley and track systems that suspend movable wall panels are: (1) to allow the walls to be moved with as little friction as possible; (2) to keep the wall panels properly centered within the track; (3) to reduce the shock caused by a trolley impacting a stationary object such as a track intersection and to allow panels to sway; and (4) to allow the panels to be moved across angular (as opposed to curved) track intersections without the trolleys dropping into gaps which usually exist in such intersections. No known system accomplishes all of these objectives.
Single puck or disc trolleys such as disclosed in U.S. Pat. No. 4,084,289 generally fail to reduce friction to an acceptable level because one side of the trolley rotates in a direction opposite to the direction the wall is moved. This problem was solved in U.S. Pat. No. 4,141,106 by using a canted puck, but such a system allows a panel to sway to an unacceptable level, and does not keep the wall panel properly centered in its track.
Another method is to use a track having a pair of flanges, which engage two vertically spaced trolleys or pucks. In U.S. Pat. No. 4,159,556, the objective of such a system was to allow the trolley to easily traverse track intersections. However, such systems require twice as much contact between the trolley and track, increasing friction. Other systems, such as those described in U.S. Pat. Nos. 3,042,960, 3,879,799 and 4,401,033, provide for upper and lower discs, with only opposite sides of the upper and lower discs engaging the track. However, such systems are not only expensive to manufacture, but do not allow a standard wheeled trolley to be used in the track if desired. Other known systems do not adequately protect the joint of a trolley and wall panel, causing such joints to quickly wear from the shock resulting when a trolley is moved in a track intersection or when a panel sways. In addition, wall panels become stuck in track intersections in other known systems because the trolleys are prone to drop into the gaps in such intersections.